Appeal No. 2003-1332 Page 7
Application No. 09/797,143
to a martensitic structure while unhardened pearlitic structures may be suitable
to provide suitable stem and seat abrasion resistance in conventional automobile
internal combustion engine use. For most engine applications, a valve made in
accordance with the present process having a Rockwell hardness on the C-scale
(Rc) on the valve tip of about 50 or more and on the other surfaces of valve of
about 20 Rc or more provides for satisfactory operation and high resistance to
wear. Since a full martensitic structure has a hardness in the range of about 50
to about 60 Rc units, a hardness in the valve tip of at least about 50 Rc can be
achieved either during the primary case hardening operation or during a
secondary localized case hardening of the tip itself such as for example by
subjecting it to a flame-hardening treatment step as schematically illustrated in
FIG. 1.
Kloske's invention pertains to steels especially adapted for use in exhaust
poppet valves for internal combustion engines, and provides a steel of novel
composition and improved properties therefor, which is further characterized over steels
which are presently commercially acceptable for such applications, in being
cold-formable, as by upsetting and extruding, into valve configuration. The steel of
Kloske's invention is essentially a substantially austenitic, medium carbon, high
nitrogen, chromium-nickel-manganese steel with 19-23% Chromium; 4.0-6.5% Nickel;
6.5-8.0% Manganese; 0-1.0% Silicon; 0.15-0.30% Carbon; 0.15-0.30% Nitrogen;
0-0.2% Columbium; 0-0.1% Phosphorous; 0-0.1% Sulphur; and the balance
substantially Iron. Kloske teaches (column 2, lines 42-49) that his steel differs
fundamentally from low carbon austenitic steels of, for example, 0.05% maximum
carbon, which are strengthened exclusively by nitrogen additions, and which require a
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